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(11) | EP 1 342 623 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | REINFORCED IMPACT BEAM |
| (57) An impact beam (100) as subject of the invention comprises a polymer matrix (15)
and a metal reinforcing structure (18), which comprises metal cords (18). The impact
beam (100) has improved impact resistance and has improved integrity during and after
impact. |
Field of the invention.
[0001] The present invention relates to impact beams and reinforcements, and a method to provide such impact beam. The invention further relates to the use of an impact beam for support of bumpers of vehicles or for impact reinforcing of parts of vehicles.
Background of the invention.
[0002] Presently known impact beams comprise a polymer matrix, reinforced with glass fibers or other polymer fibers.
An impact beam may also comprise metal parts, usually on the places where the impact beam receives compression load during impact. US-A-5 290 079 gives an example of such impact beam. In US-A-5 290 079 the impact beam also comprises a woven wire mesh, which is to improve the ductility and flexibility of the impact beam.
[0003] Presently known impact beam in general have the disadvantage that they tend to break or in two parts at the location of impact, or into several small particles which are projected towards objects which are in the periphery of the impact beam. This may cause further damage to these objects.
Summary of the invention.
[0004] It is an object of the present invention to provide an improved impact beam having increased resistance to impact and guarantying an improved integrity during and after impact.
[0005] An impact beam as subject of the invention comprises a polymer matrix and a metal reinforcing structure. According to the present invention, the metal reinforcing structure comprises at least two, but preferably more than two metal cords being preferably essentially parallel to each other.
[0006] An impact beam is characterized by a direction in which impact forces are expected to work on the impact beam. This direction is hereafter referred to as 'impact direction'. Impact beams are characterized by an impact plane, being the plane perpendicular to the direction of impact. One dimension of this plane is usually relatively large and is hereafter referred to as length of the impact beam. . The second dimension of the impact beam in this impact plane, is usually much smaller than the length. This direction is hereafter referred to as height of the impact beam. The dimension of the impact beam, perpendicular to impact plane t is referred to as thickness of the impact beam.
[0007] The metal cord of an impact beam as subject of the invention may be provided in a direction essentially parallel to the length of the impact beam.
[0008] Most preferably however, the metal cords are provided with a curved shape during molding of the impact beam as subject of the invention. The curves have a bending radius in the plane perpendicular to the plane defined by the length and height, and parallel to the length of the impact beam. The curvature preferably extends to the side of the impact beam on which the impact force is to be expected to work.
[0009] The metal cord preferably used for an impact beam as subject of the invention, are of a type which can absorb relatively high amounts of impact energy but also other metal cords may be used.
[0010] Examples here are:
- multi-strand metal cords e.g. of the m x n type, i.e. metal cords, comprising m strands with each n wires, such as 4x7x0.10 or 3x3x0.18; the last number is the diameter of each wire, expressed in mm.
- compact cords, e.g. of the 1 x n type, i.e. metal cords comprising n metal wires, n being greater than 8, twisted in only one direction with one single step to a compact cross-section, such as 1x9x0.18 or 1x12x0.18; the last number is the diameter of each wire, expressed in mm.
- layered metal cords e.g. of the l + m (+ n) type, i.e. metal cords with a core of l wires, surrounded by a layer of m wires, and possibly also surrounded by another layer of n wires , such as 2+4x0.18; the last number is the diameter of each wire, expressed in mm.
- single strand metal cords e.g. of the 1 x m type, i.e. metal cords comprising m metal wires, m ranging from two to six, twisted in one single step, such as 1x4x0.25; the last number is the diameter of each wire, expressed in mm.
- Open metal cords e.g. of the m+n type, i.e. metal cords with m parallel metal wires surrounded by n metal wires, such as disclosed in US-A-4408444, e.g. a metal cord 2+2x0.25; the last number is the diameter of each wire, expressed in mm.
[0011] All cords as described above can be equipped with one or more spiral wrapped wires to increase the mechanical bond of the cords in the polymer matrix, and/or to bundle the n single parallel crimped or non-crimped but plastically deformed wires if the cord is provided using such parallel wires.
Preferably however, the metal cord used in the context of the present invention may be a metal cord with a high elongation at fracture, i.e. an elongation exceeding 4 %, e.g. an elongation between 5% and 10%. High elongation metal cord has more capacity to absorb energy.
[0012] Such a metal cord is:
- either a high-elongation or elongation metal cord (HE-cords), i.e. a multi-strand or single strand metal cord with a high degree of twisting (in case of multi-strand metal cords : the direction of twisting in the strand is equal to the direction of twisting of the strands in the cord : SS or ZZ, this is the so-called Lang's Lay) in order to obtain an elastic cord with the required degree of springy potential ; an example is a 3x7x0.22 High Elongation metal cord with lay lengths 4.5 mm and 8 mm in SS direction;
- or a metal cord which has been subjected to a stress-relieving treatment such as disclosed in EP-A1-0 790 349 ; an example is a 2x0.33 + 6x0.33 SS cord.
- as an alternative or in addition to a high elongation metal cord, the metal cord may be composed of one or more wires which have been plastically deformed so that they are wavy. This wavy nature additionally increases the elongation. An example of a wavy pattern is a helix or a spatial crimp such as disclosed in WO-A1-99/28547.
[0013] According to the required properties of the impact beam as subject of the invention, all metal cords may be identical, or alternatively, different metal cords may be used to provide the impact beam.
[0014] Most preferably steel cords are used to provide the impact beam as subject of the invention. Presently known steel alloys may be used to provide the steel cords. Preferably, the steel cords are subjected to a stress relieving thermal treatment, e.g. by passing the steel cord through a high-frequency or mid-frequency induction coil of a length that is adapted to the speed of the steel cord during production. It was observed that, increasing the temperature to more than 400°C for a certain period of time, a decrease in tensile strength of the steel cord (a reduction of approximately 10%), but at the same time, an increase of the plastic elongation of the cord before rupture of more than 6% may be obtained. Such steel cords are hereafter referred to as stress relieved steel cords.
[0015] An impact beam as subject of the invention comprises a polymer matrix, preferably chosen out of the group of thermoplastic semi-crystalline polymers such as polypropylene, polyamide, polyester, polyethyleneterephtalate, polybuteneterephtalate as well as blends of these materials.
The polymer matrix preferably comprises at least two layers.
The first layer, hereafter referred to as 'embedding layer' makes contact to the metal cord surfaces. Such embedding layer may be extruded around the metal cord, or several metal cords may be bundles and provided with an embedding layer coating. Alternatively, several metal cords are laminated in one plane between two foils of polymer material, providing a tape-like structure, hereafter generally referred to as 'metal cord tape', or steel cord tapes in case the metal cord tape is provided using steel cords.
[0016] Around this metal cord with embedding layer, a second layer, hereafter referred to as volume layer, may be provided, e.g. by extrusion or in a molding process.
[0017] The polymer material of the embedding layer is preferably chosen out of the group of thermoplastic semi-crystalline polymers such as polypropylene, polyamide, polyester, polyethyleneterephtalate, polybuteneterephtalate as well as blends of these materials, or thermoplastic elastomers , e.g. polyamide- or polyolefin-based thermoplastic elastomers such as polyesteramides, polyetheresteramides, polycarbonate-esteramides or polyether-block-amides..
[0018] The polymer material of the volume layer is preferably chosen out of the group of thermoplastic semi-crystalline polymers such as polypropelyne, polyamide, polyester, polyethyleneterephtalate, polybuteneterephtalate as well as blends of these materials. This volume layer may further comprise glass or C-fibers and/or mineral fillers to reinforce the volume layerFibers can either be random, unidirectional, chopped, or a combination of those. The plastic elongation of the polymer matrix may be limited to only 4% by adding such fibers or fillers.
[0019] In order to assure a good adhesion between the metal cords and the polymer material, an adhesion promoter can be applied on the metal cords.
Possible adhesion promoters are bifunctional coupling agents such as silane compounds. One functional group of these coupling agents is responsible for the binding with the metal or metal oxides; the other functional group reacts with the polymer.
[0021] In order to improve the impact resistance to the required level, the amount of metal cord per section of the impact beam as subject of the invention in a direction defined by the height and thickness of the impact beam, may be chosen.
[0022] Best results are obtained when the metal cords are arranged in one or more planes, parallel to each other and to the impact plane of the impact beam, or one or more planes parallel to each other and being provided with a curved shape during molding of the impact beam. The curvature preferably extends to the side of the impact beam on which the impact force is to be expected to work.
Each plane may be provided by means of a metal cord tape or steel cord tape, having embedding layers which may be equal or different from each other. Each plane may each plane may comprise metal or steel cords, being equal or different from each other.
[0023] An impact beam as subject of the invention may be manufactured using different production techniques.
[0024] Preferably however, a polymer matrix sheet, most preferably a Glass Mat Reinforced Thermoplastic Prepreg is used. The glass mat reinforced thermoplastic prepreg can either obtain random longfiber, unidirectional or chopped fiber materials or combinations of these. Similarly, long fiber thermoplastic compounds can be used comprising chopped strand glass fibers.
This glass mat reinforced thermoplastic prepreg is heated during a glass mat reinforced thermoplastic prepreg-heating step, using any kind of oven system until the thermoplastic resin melts. In case of long fiber thermoplastic compound, an extruder is used to provide polymer matrix, hereafter referred to as the long fiber thermoplastic compound extrusion step.
[0025] Preferably, although not always necessarily, the metal cords or metal cord tapes may also be heated during a metal cord heating step, using any kind of oven or by induction heating.
[0026] After the glass mat reinforced thermoplastic prepreg-heating step and possibly a metal cord heating step, the metal cords or metal cord tape and the glass mat reinforced thermoplastic prepreg are brought together, usually by providing the polymer matrix or glass mat reinforced thermoplastic prepreg around the metal cord or metal cord tape, and provided to a compression molding tool. The metal cord or metal cord tape and glass mat reinforced thermoplastic prepreg together are subjected to a molding step. The metal cord or metal cord tape are positioned in the location of the section of the profile where it is intended to be located to obtain the maximum performance. During the closing of the mold, the glass mat reinforced thermoplastic prepreg flows and encapsulates the metal cord or metal cord tape within the polymer material of the glass mat reinforced thermoplastic prepreg. Possibly, the metal cords or the metal cord tape is provided with a curved shape.
[0027] After the mold is closed, the mold and molded material is cooled during a cooling step. the mold is re-opened. An impact beam as subject of the invention is so provided.
[0028] The same molding process can be used, but the oven is replaced by an extruder which produces blobs of hot lofted glass-filled thermoplastics or long fiber thermoplastic compound that are then manipulated into the tool or mold, in case an long fiber thermoplastic compound extrusion step is used.
[0029] Alternatively, glass and/or other fiber strands and metal cords or metal cord tape may be subjected to a pultrusion process in order to provide an impact beam as subject of the invention. First fiber strands and/or reinforcing fabrics and metal cords or metal cord tape are provided. Uncured or not fully cured thermoplastic material is provided to these fiber strands and/or reinforcing fabrics and metal cords or metal cord tape by drawing them through a bad of uncured or not fully cured thermoplastic material. Then the fiber strands and/or reinforcing fabrics and cords and uncured or not fully cured thermoplastic material are drawn through a heated pultrusion die. This causes curing of the thermoplastic material a pultruded article s so provided. The pultruded article is cut into lengths. Each cut length is than an impact beam as subject of the invention.
[0030] Alternatively, glass and/or other fiber strands and metal cords or metal cord tape may be subjected to an overextrusion process in order to provide an impact beam as subject of the invention. Metal cords or metal cord tapes are provided and brought in an extrusion mold and position in the mold. Thermoplastic material is provided in the extrusion mold, e.g. by extrusion. The mold comprises now an impact beam, which is to be cooled. Possibly, the thermoplastic material comprises glass fibers, next to the polymer material, which is or fully, or partially or not cured.
[0031] The impact beam as subject of the invention may further comprise openings for fixings or mounting other objects. These openings can be brought into the impact beam by punching, drilling, CNC, laser cutting or similar techniques, but also by means of inmold punching.
[0032] Best impact resistance is obtained when the metal cords are embedded in the polymer matrix, having either one or more layers, in such a way that they have a limited freedom to elongate and/or untwist during impact.
Depending on the type of the metal cord construction, a relatively large amount of impact energy may be adsorbed depending on the impact adsorption mechanism, which is typical for that metal cord construction.
[0033] High elongation (HE-) cords can adsorb impact energy by the structural deformation of the cords due to movements of strands one to another in the cord. When structurally deformed filaments are used to provide the metal cords, also the removing of the structural deformation out of the filaments during elongation of the metal cord will cause an adsorption of the impact energy. In case the metal cord is a stress relieved steel cord, also the plastic deformation of the filaments will provide an adsorption of impact energy.
[0034] The polymer matrix is bound to the metal cord either by means of a chemical, a mechanical or a combination of chemical and mechanical bond. During a local impact, the polymer matrix, eventually by means of an embedding layer and a volume layer, distribute the local force over the full cord length. This results in a full use of the cord's energy adsorption abilities hence the energy to be adsorbed by other parts outside the beam is reduced and local breakage of the polymer matrix is postponed. The energy adsorption of the cord is either through plastic stretching of the cord itself, through torsional deformation of the cord such as untwisting, or energy dissipation interface between cord and polymer layer due to friction when a relative movement of cord versus matrix is taking place.
If the impact force is such that the local stresses in the polymer matrix exceed its breaking strength the polymer matrix will fall apart into pieces which still adhere to the metal cords. This falling apart will adsorb a limited amount of impact energy, but after this falling apart, the metal cords may elongate to a larger extent and will be able to adsorb to a large extent all impact energy possible until they break.
[0035] Alternatively, when a polymer matrix comprising an embedding layer and a volume layer, this volume layer preferably will fall apart first by impact. The pieces adhere to the embedding layer and allow the embedding layer and the metal cords to extend to some extent. Then possibly the embedding layer will fall apart but will adhere to the metal cords. These metal cords can then elongate and adsorb the impact energy, which is still left.
When an impact beam with several metal cord tapes are used , all parallel to each other, the bond between two metal cord tape may be broken. Impact energy may then be adsorbed due tot he friction caused by the relative movement of both metal cord tape relatively to each other.
[0036] An impact beam as subject of the invention may be used to support soft bumpers of vehicles such as cars, busses or trucks. It may also be used to improve the impact resistance other elements of the vehicle's coachwork to impact forces. Impact beam as subject of the invention may be used to make e.g. doors, frame, bonnet or hood and or cross beams more impact resistant. A person skilled in the art understands that the shape of cross sections of an impact beam as subject of the invention, as well as the outer shape of the impact beam, may be adjusted to the use of the impact beam.
The impact beam as subject of the invention absorbs the impact energy and protects the other elements of the vehicle for damaging. The impact beam as subject of the invention also prevents the particles of the polymer matrix to damage peripherical elements of the vehicle, since the integrity of the impact beam after impact can be secured.
Brief description of the drawings.
[0037] The invention will now be described into more detail with reference to the accompanying drawings wherein
- FIGURE 1 a being a schematical view of a cross section of an impact beam as subject of the invention
- FIGURE 1b being a schematical front view of an impact beam as subject of the invention.
- FIGURE 2, FIGURE 3 and FIGURE 4 being a schematical view of a cross section of an alternative impact beam as subject of the invention.
- FIGURE 5 being a scheme of a method to provide an impact beam as subject of the invention.
- FIGURE 6 shows schematically the use of an impact beam as subject of the invention to support a vehicle bumper.
Description of the preferred embodiments of the invention.
[0038] An impact beam as subject of the invention is schematically shown in FIGURE 1a and FIGURE 1b.
[0039] An impact beam 100 has a length 11, which is substantially larger than the height 12 and the thickness 13 of the impact beam 100. The embodiment as shown in FIGURE 1 has a thickness that is provided by a pair of legs 14 and a main volume 15. The legs 14 may be used to fix the impact beam to other parts of the object to which it is to be mounted, whereas the main volume 15 (with its thickness 16) will adsorb most of the impact energy provided by an impact in direction as indicated with arrow 19.
[0040] The main volume 15 and the legs 14 comprise a polymer matrix. In the main volume 15, metal cords 18 are present in a direction essentially parallel to the length 11 of the impact beam 100. Preferably all metal cord are present in one or more planes 10.
The metal cords 18 used to provide the metal cord tape were 7x7 cords, being a core strand of a filament of 0.21mm, round which 6 filaments of 0.19mm are twisted. Around this core strand, 6 strands are twisted, each strand comprising a core filament of 0.19mm around which 6 filaments of 0.175mm are twisted.
[0043] FIGURE 2 shows an impact beam as subject of the invention which comprises around metal cord 18 an embedding layer 21 of polymer matrix and a second so-called volume layer 21 of polymer material.
[0044] The metal cord are provided by means of a metal cord tape 23 which is provided in a plane essentially perpendicular to the impact direction 19. The metal cords used to provide the metal cord tape were 7x7 cords, being a core strand of a filament of 0.21mm, round which 6 filaments of 0.19mm are twisted. Around this core strand, 6 strands are twisted, each strand comprising a core filament of 0.19mm around which 6 filaments of 0.175mm are twisted.
Type polymer material of the embedding layer 20 was a polyolefin based thermoplastic elastomer.
[0045] Type polymer material of volume layer 21 is glass fiber filled semi-crystalline Polyporpylene.
[0046] FIGURE 3 shows another alternative embodiment of an impact beam
as subject of the invention. The metal cords 18 are provided by means of two metal cord tapes 31 and 32, which are provided parallel to each other and essentially parallel to the impact direction 19.
[0047] FIGURE 4 shows an improved impact beam as subject of the invention where the legs 41 and main volume 42 are connected to each other by means of a transition zone 43. Several metal cord tapes 44 and possible individual metal cords 45 may be used to provide impact resistance in both the main volume 42 or the transition zone 43.
[0048] Turning now to a method to provide an impact beam as subject of the invention, such method is schematically shown in FIGURE 5.
[0049] First a glass mat reinforced thermoplastic prepreg 500 is provided comprising polymer matrix 501 and possibly glass fiber mat 502 (step 50). Also metal cords 503 are provided preferably having an adhesion layer 504 around the surface of the metal cords 503. Most preferably the metal cord and adhesion layer are provided as a metal cord tape 505. (step 51).
[0050] As shown in step 52 of FIGURE 5, the glass mat reinforced thermoplastic prepreg 500 is heated to soften the polymer material 501 using a furnace 506. glass mat reinforced thermoplastic prepreg may be supported and transported trough the furnace using a transporting means e.g. a belt 507. After being heated, the hot glass mat reinforced thermoplastic prepreg is taken of the transporting means as indicated with arrow 508, and is provided for addition to the metal cord tape in step 54.
[0051] As shown in step 53 of FIGURE 5, the metal cord tape 505 may be heated to soften the polymer material 504 using a furnace 509. metal cord tape may be supported and transported trough the furnace using a transporting means e.g. a belt 510. Possibly after being heated, the metal cord tape is taken of the transporting means as indicated with arrow 508 and is provided for addition to the metal cord tape in step 54. A skilled man understands that in case the metal cord or metal cord tape is not to be heated, they may be provided to step 54 with no handling as in step 53.
[0052] In step 54, the metal cords or metal cord tape 505 and the hot glass mat reinforced thermoplastic prepreg 500 are brought together, e.g. by adding or stacking the different layers one on top of the other.
[0053] The stack 511, comprising the glass mat reinforced thermoplastic prepreg 500 and the metal cord or metal cord tape 505 are provided to a mold comprising two parts, being the female mold 512 and the male mold 513 (step 55a). The molds 512 and 513 are closed (step 55b) and the stack 511 is bend and shaped to the open area inside the closed mold.
[0054] After this molding (step 55a and 55b) the mold and the shaped impact beam is cooled to a temperature for which the polymer material 501 is solidified (cooling step 56). The impact beam may then be taken out of the molds and is ready for further processing, such as quality control or provision of additional openings.
[0055] An impact beam as subject of the invention is so provided, which may be used as support for soft bumpers of vehicles, as shown in FIGURE 6.
[0056] An impact beam 61 is connected to peripheral elements 62 of the vehicle caochwork. A soft bumper element 63 may be provided covering the impact beam 61. when the vehicle strikes an object, an impact force with a direction 64 will apply in as indicated in FIGURE 6.
[0057] The metal cord present in the impact beam 61 will adsorb the impact energy to a large extent, and the polymer material of the impact beam will adhere to the metal cord to a large extent. This to avoid that particles of the polymer material will be projected further towards the parts of the vehicle which are located behind the impact beam.
1. An impact beam comprising a polymer matrix and a metal reinforcing structure, characterized in that said metal reinforcing structure comprises metal cords.
2. An impact beam as in claim 1, wherein said polymer matrix being a semi-crystalline
thermoplastic polymer.
3. An impact beam as in claim 1 or 2, wherein said metal cords being steel cords.
4. An impact beam as in claim 1 to 3, wherein said metal cords being essentially parallel
to each other.
5. An impact beam as in claim 1 to 3, wherein said metal cords being arranged in one
or more planes, said planes being essentially parallel to eachother.
6. An impact beam as in claim 1 to 5, wherein said polymer matrix comprising at least
two layers, a first layer being present around the surface of said metal cords, and
a second layer being present around said first layer.
7. An impact beam as in claim 6, wherein said first layer being made out of thermoplastic
polymer selected from the group consisting of thermoplastic elastomer, polypropylene,
polyamide, polyester, polyethyleneterephtalate, polybuteneterephtalate or blends of
these materials.
8. An impact beam as in claim 6 or 7, wherein said second layer being made out of thermoplastic
polymer selected from the group consisting of polypropylene, polyamide, polyester,
polyethyleneterephtalate, polybuteneterephtalate or blends of these materials.
9. An impact beam as in claim 1 to 8, wherein said metal cords do not have a chemical
bond with said polymer matrix.
10. An impact beam as in claim 1 to 8, wherein said metal cords do have a chemical bond
and a mechanical bond with said polymer matrix
11. A method for providing an impact beam, said method comprising the steps of
- providing a polymer matrix sheet;
- providing metal cords;
- heating the polymer matrix sheet;
- bringing the metal cords and polymer matrix sheet together and providing the metal cords and polymer matrix sheet to a mold;
- molding the metal cords and polymer matrix sheet, providing an impact beam;
- cooling the impact beam.
12. A method as in claim 11, said polymer matrix sheet comprising glass fibers.
13. A method for providing an impact beam, said method comprising the steps of
- providing metal cords;
- extruding polymer material and providing extruded polymer material to said metal cords;
- bringing the metal cords and polymer matrix sheet together and providing the metal cords and polymer matrix sheet to a mold;
- molding the metal cords and polymer matrix sheet, providing an impact beam;
- cooling the impact beam.
14. A method for providing an impact beam, said method comprising the steps of
- providing fiber strands and/or reinforcing fabrics;
- providing metal cords,
- providing uncured or not fully cured thermoplastic material to said fiber strands and/or said reinforcing fabrics and said metal cords by drawing said fiber strands and/or said reinforcing fabrics and said metal cords, through a bath of uncured or not fully cured thermoplastic material;
- curing said fiber strands and/or said reinforcing fabrics and said metal cords and said uncured or not fully cured thermoplastic material by drawing said fiber strands and/or said reinforcing fabrics and said metal cords and said uncured or not fully cured thermoplastic material through a heated pultrusion die, so providing a pultruded article;
- cutting pultruded article to lengths, so providing an impact beam.
15. A method for providing an impact beam, said method comprising the steps of
- providing metal cords;
- bringing the metal cords in an extrusion mold and position the metal cords in the mold;
- providing thermoplastic material in the extrusion mold to provide an impact beam;
- cooling the impact beam.
16. A method as in claim 15, said method further comprising the step of providing glass
fiber and positioning glass fibers in said extrusion mold.
17. A method as in claim 13 to 16, said thermoplastic material further comprising glass
fibers.
18. A method as in claim 11 to 17, wherein said metal cords are provided as a metal cord
tape, comprising metal cords and a polymer matrix around said metal cords.
19. A method as in claim 11 to 18, wherein said method further comprising the step of
heating the metal cords or metal cord tape.
20. Use of an impact beam as in claim 1 to 10 for support of bumpers of vehicles or to
improve the impact resistance of vehicle's coachwork.
21. Use of an impact beam obtainable by using a method as in claim 11 to 19 for support
of bumpers of vehicles or to improve the impact resistance of vehicle's coachwork.